Production of ferric oxide



oct. 17,1939. .u E. BOWES 2,176,242

PRODUCTION oF FERRIC OXIDE n original Filed June 26, 1934 V 71755/0053/i y' l INVENTOR ATTO RN EY Patented Oct. 17, 1939 UNITED STATES PATENTOFFICE Application June 26, 1934, Serial No. 732,488 Renewed April 20,1938 Claims.

This invention relates to the art of metallurgy and has particularreference to a method for removing a metal from its ores or mixtures inwhich it is contained, the metal being obtained 5; either in a purestate or in a form in which it may be commercially used.

One of the primary objects of this invention is to provide a method ofthe above mentioned character which will produce the metal or the 1Qdesired compound thereof in a form possessing a high degree of purity.

A further object of this invention is to provide a method of the abovementioned character which may be carried out at temperatures l lowerthan those temperatures generally heretoi fore required for the recoveryof metals and their compounds.

Still further, the invention has as an object to provide a method whichwill eliminate the use 2Q of expensive re-agents which become lost orconsumed during the process and to thus provide a method or processwhich may be economically carried out on a commercial scale.

Numerous other objects and advantages of the 25 invention will becomeapparent as the following description proceeds.

For the purpose of clearly presenting the invention, the same will bedescribed as being embodied in a process for removing iron from ores 30or mixtures in which it is contained, but it is to f be understood thatthe invention is not limited to the recovery of iron alone but may beutilized in the recovery or obtaining of other metals and theircompounds.

35 The usual method of recovering iron from iron ore is by the blastfurnace, which has two main functions. One function of the blast furnaceis to cause a reduction of the iron oxide to free iron by allowing fixedcarbon and carbon monoxide 40 to combine with the oxygen of the ironoxide. The second main function of the blast furnace is to'separate theiron from the non-ferrous portion of the ore, chiefly silica but alsolesser amounts of other impurities, by adding lime which reacts 45 withsilica and alumina to form a glass or slag Y which is less dense thaniron and will float on the molten iron. Since the iron is in a moltenstate during the process, the separation is not complete for the reasonthat carbon and certain 50 other impurities generally present in the oreare soluble in the molten iron to some degree.

While the reduction o f iron oxide to free iron can be accomplished at arelatively low heat, approximately 1200 to lelOOc F., the separation of5 5 the iron from the non-ferrous portions of the ore cannot beaccomplished at this low temperature, with the result that the blastfurnace which performs both functions or steps of the process is usedpractically universally. The use of blast furnaces however, has certainfundamental ds- 5 advantages, chief among which are the followmg:

First, excessively high temperatures are required to fuse theslag-forming materials at a desirable rate, the temperatures ordinarilyused being above 2800o F. even though the reduction of the iron oxidecould be accomplished at a temperature between 1200 to 1400 F. This hightemperature requires the use of coke which is a relatively expensiveform of fuel as compared to coal, which could be utilized for reductionof the iron oxide at a red heat.

Further, the emciency of the blast furnace decreases rapidly with thedecrease of iron content in the ore or the mixture being treated becauseof the great increase of heat required to slag the additional silica.Thus the blast furnace is not really suited for the processing of lowgrade ores.

Further, as brought out before, carbon and certain other impuritiesdissolve in the molten Viron and most of these impurities must later beremoved in the making of steel. In practice it is found thatapproximately 4% of the carbon from the coke which is utilized dissolvesin the molten 1ron.

A still further disadvantage of the blast furnace is that in thisprocess limestone must be used for forming the slag and this limestoneconstitutes a substantial item of cost in the process.

The present invention contemplates the elimination of the abovementioned disadvantages and the provision of a practical method whichmay be continuously and economically performed.

In its broader aspects the method consists in treating ore containingiron with a re-agcnt which reacts with the iron to convert the same to agas, and to form an accompanying gas, separating this gasiied iron andthe accompanying gas from, the ore, and reversing the reaction 5 whichoccurred during the initial conversion of' the iron to a gas to convertthe gasied iron to a solid form and to recover the re-agent utilized inthe original conversion. Thus the method broadly consists in subjectingthe iron while in a gaseous state to reversible reactions, the productthus produced being a pure iron oxide which may be subsequently reducedat a red heat to obtain iron of a high degree of purity which is notcontaminated with the impurities ordinarily taken up by the molten ironin blast furnace practice.

More specifically the method consists in rst preheating the iron ore ormixture to be treated to a suitable temperature, approximately 1800 to2000 F. This can be done cheaply and the temperature may be keptsufciently low that the iron is not converted into a molten condition.

The next step in the process consists in effecting a contact of agaseous re-agent with the heated ore to convert the iron to a gaseousstate and to produce an accompanying gas. This is effected in anatmosphere free from air, and a gasifying re-agent is utilized which isa gas at or above the temperatures employed at atmospheric pressure. Anexample of such a re-agent is hydrogen chloride. It is important thatthe reagent utilized be such that it will combine with the iron but willnot combine with the nonferrous portion of the ore.

The gasied iron compound is then separated from the residue of the oreand after its separation is subjected to a somewhat lower temperatureapproximately 1200 to 1600 F. This causes the gaseous iron compound andthe accompanying gas to react forming crystals of ferric oxide andcausing the hydrogen chloride to return to its original form so thatthis re-agent may be recovered and again utilized.

The several reactions which take place in the process as thus fardescribed are probably illustrated by the following equations.

The rst equation indicates the reaction which takes place when the ironoxide in the ore is converted into a gas. The hydrogen chloride which isa gas at and above atmospheric temperatures contacts with the iron oxidein the ore with the result that ferric chloride and water are formed asindicated by the equation. The ferric chloride volatilizes above 5,75 F.so that the iron in gaseous form is separated from the silica and otherimpurities in the ore. The water which is formed during this reactiontravels with the ferrie chloride in the form of steam in view of thetemperature at which this reaction is effected.

The steam and ferric chloride both being gases or vapors are, as broughtout before, separated from the residue of the ore and these gases orvapors are then subjected to the lower temperature preferably from 1,200to 1600 F. at which time the reaction indicated as Equation 2l abovetakes place. By reference to this equation it will be noted that thehydrogen chloride returns to its original form so that it may besuitably recovered for further use while the iron oxide in a pure statecrystallizes and may be separated from the gaseous hydrogen chloride.The reversing reaction by which the iron chloride changes to acrystalline iron oxide may occur at various temperatures preferablybetween those above mentioned depending upon time and equilibriumfactors.

The iron oxide as thus obtained is substantially pure and the processmay be terminated at this point, the iron oxide being disposed ofcommercially for whatever purposes it is desired to use the same. If,however, pure iron is desired, the pure iron oxide which has beenobtained may be readily reduced at a red heat in any desired manner, asfor example, by the use of carbon. It will be apparent that thisreduction of the iron oxide to pure iron may be accomplished without theuse of expensive fuel and that in View of the fact that the iron is notconverted into a molten condition during this reducing operation thereis. no danger that carbon or other impurities will be combined with ordissolved in the iron.

While numerous types of apparatus might be utilized for carrying out theabove process, there is diagrammatically illustrated in the singlefigure of the drawing one form of apparatus which may be readilyutilized.

Referring then to the drawing, the numeral I designates generally achamber adapted to receive the ore to be treated. It is in this chamberthat the primary reaction takes place in that the gasifying reagent isforced upwardly through the ore in chamber il), converting the iron toferric chloride and leaving the non-metallic portion of the ore in thechamber. The chamber I0 is defined by the side walls Il and terminatesat its lower end in a hopper l2 into which the gangue or non-metallicportions of the ore falls. A closed screw conveyor i3 communicates withthe lower end of the hopper I2 for removing the non-metallic portion ofthe ore from the hopper.

For feeding the ore to be treated to the chamber lil there is provided aclosed hopper I5, the discharge end I6 of which projects slightly withinthe open upper end of the chamber l0. Ore which has been previouslyheated in a rotary kiln or by some other external heating device is fedinto the hopper i by conduit Il, the hopper I5 being kept partly full ofthe ore to prevent the escape of gas from the retort 20.

The retort 20 comprises the side walls 2l, which merge into a top wallsnugly embracing the discharge end IB of the hopper l5 as illustrated.The retort thus provides a chamber 23 which surrounds the chamber il]and which communicates at its upper end with the upper end of chamberID. The chamber 23 defines the zone of reverse reaction in which thecrystals are deposited from the reaction of the gases leaving chamberIl).

The floor of the retort is provided with hoppers 25 and each hopper isprovided with a closed screw conveyor 2B by which the crystals whichcollect in the hoppers 25 may be removed. The walls 2| and 22 of theretort are formed of a refractory material and the inner surfaces ofthese walls are salt-glazed while the exterior surfaces are suitablycovered to be impervious to the penetration of gases.

Tapped into the retort is a conduit 30 which communicates with a bloweror fan 3| which functions to withdraw gas from the retort and todischarge the same into the lower end of chamber l0 by means of asuitable conduit 32. The conduit 32 is provided on its end with asuitably shaped nozzle 33 to aid in properly dis.- tributing thegasifying re-agent across the lower end of chamber lil. A valvecontrolled conduit 31% may, if desired, be tapped into the conduit 30for supplying additional quantities of the gaseous re-agent to thesystem when necessary.

In carrying out the process` with the apparatus illustrated and assumingthat the chambers l0 and 23 and the hopper l5 are all empty, the rststep is to remove the air from these chambers and the hopper. This maybe conveniently accomplished by actuating the blower 3i sufciently toremove the air from the blower and by admitting hydrogen chloride to thesystem by means of conduit 3A. The hydrogen chloride being heavier thanair will settle to the bottom of the chambers l and 23 causing the airto escape through the hopper I and conduit Il. After all of the air hasbeen exhausted the valve in conduit 34 is closed so that the chambers I0and 23 and the hopper I5 are all filled with hydrogen chloride atsubstantially atmospheric pressure.

'Ihe iron ore or other mixture containing iron is then preheated in anydesired manner to a temperature between 1600 and 2000" F. and is fedinto the hopper I5 by way of conduit I1. The heated ore falls from thehopper I5 through ythe discharge I6 into the chamber IIJ filling thelatter as indicated. The fan 3| may then be rstarted causing thegasifying re-agent to be withdrawn from chamber 23 and forced upwardlythrough the ore in chamber ID.

As brought out before the chamber I0 defines the primary reaction zonewhile the chamber 23 defines the zone of reversereaction in whichcrystals are deposited from the reaction of gases. Thus in the chamberI0 the gaseous re-agent is forced upwardly through the iron ore andcombines with the iron to form gaseous ferric chloride and steam. Thesetwo gases flow out the open upper end of chamber Ill leaving thenonferrous portion of the ore which includes silica and otherimpurities, remaining in chamber I0 to be withdrawn therefrom byconveyor I3. It might be noted that by feeding the hot ore into the topof chamber I0 and the re-agent into the bottom of this chamber, a veryefficient conversion of the iron oxide of the ore to ferrie chloride maybe eiected because the ore is hottest at the point of exit of the gasesfrom the chamber I5. The chamber 23 is at a temperature lower than thechamber I0, the temperature maintained in chamber 23 being between 1200and 1600" F. As the steam and the gaseous ferric chloride thereforereach chamber 23 the reverse of the chemical reaction takes placeproducing pure ferric oxide and the original hydrogen chloride. The purecrystals of ferric oxide (haematite) fall into the hoppers 25 and arewithdrawn from these hoppers by the conveyors 26 while the gasifyingre-agent is withdrawn from the chamber 23 by conduit 30 and isrecirculated through the chamber I0.

It is preferable to maintain the pressure within the chambers I0 and 23substantially the same as that of the atmosphere to thus reduce thepossibility of air entering these chambers or the .gasifying re-agentfrom escaping from these chambers. To further guard against theadmission of air into or the escape of the re-agent from the chambers I0and 23, the hoppers I2, I5 and are all kept partly full as indicated.

To facilitate the reversible reactions previously described, it ispreferable that there be no excess of hydrogen chloride Within thechamber 23. Thus the hydrogen chloride should be fed upwardly throughchamber I0 at only such a rate as to permit all of the hydrogen chloridegas to be converted to ferric chloride gas. Approximately 1000 cubicfeet of gas fed into chamber I Il for approximately every eighty poundsof ore containing approximately 50% iron fed into the chamber shouldgive the desired results.

The pure iron crystals as thus obtained may, as brought out before, bedistributed commercially or may be further subjected to reduction at redhead to obtain iron of a high degree of purity. By virtue of the factthat this reducing operation may be elected without melting the iron,all danger of carbon or other impurities being dissolved in the iron iseliminated so that extremely pure iron may be obtained.

From the above it will be apparent that the invention provides a methodby which pure iron or iron oxide maybe conveniently and efficientlyrecovered from iron ores or other mixtures containing iron by areversible reaction in gaseous state. The recovery of the iron or ironoxide may be effected at relatively low temperatures thus eliminatingthe necessity of utilizing coke which is relatively expensive ascompared to coal. Further, the recovery may be effected withoututilizing limestone which is also relatively expensive and which isnecessary for use in the blast furnace process. The process may becontinuously carried out and since the temperatures utilized during theentire process are below the melting point of iron oxide, there is nodanger of carbon or other impurities being dissolved in the iron thusproviding for the production of iron or iron oxide of a high degree ofpurity.

While the invention has been described with some detail, it is to beunderstood that the description is for the purposes of illustration onlyand is not denitive of the limits of the inventive idea. The right isreserved to make such changes in the steps of the method and in the typeof apparatus used as will fall within the purview of the attachedclaims.

What I claim as my invention is:

1. In a method of obtaining ferric oxide from va composition in which itis contained, those steps which consist of flowing hydrogen chloridethrough a mass of the composition at a temperature above the temperatureat which ferric chloride volatilizes, to produce a gaseous mixture offerric chloride and steam, separating the said gaseous mixture from saidcomposition, lowering the temperature of the said mixture to reverse theoriginal reaction a substantial degree and produce hydrogen chloride andferrie oxide, and so limiting the amount of hydrogen chloride inproportion to the gaseous ferric chloride formed that after separatingthe gaseous ferric chloride and steam from the mass a substantial degreeof reversal of the original reaction is effected on the lowering of thetemperature of the mixture of ferrie chloride and steam.

2. In a method of obtaining continuously ferric oxide from a compositionin which it is contained, those steps which consist of owing hydrogenchloride through a mass of the composition at a temperature above thetemperature at which ferric chloride volatilizes, to produce a gaseousmixture of ferric chloride and steam, separating the said gaseousmixture from said composition, lowering the temperature of the saidmixture to reverse the original reaction a substantial degree andproduce hydrogen chloride and ferric oxide, so limiting the amount ofhydrogen chloride in proportion to the gaseous ferric chloride formedthat after separating the gaseous ferrie chloride and steam from themass, a substantial degree of reversal of the original reaction iseffected on the lowering of the temperature of the mixture of ferriechloride and steam, and recirculating the hydrogen chloride formed bythe said revers-al back into said mass for the treatment of furtheramounts of the composition.

3. In a method of obtaining ferric oxide from a composition in which itis contained, those steps which consist in heating the composition to atemperature below the melting point of ferric oxide but above thetemperature at which ferric chloride volatilizes, eifecting a contact ofhydro- Lio gen chloride gas with the heated composition to produce agaseous mixture of ferric chloride and steam, separating the gaseousmixture from said composition, lowering the temperature of the gaseousferric chloride and steam to a temperature above the temperature atwhich ferric chloride condenses, so limiting the hydrogen chloride gasutilized in proportion to the gaseous ferrie chloride formed that afterseparating the ferrie chloride and steam from the composition, asubstantial degree of reversal of the original reaction is' effectedupon the lowering of the temperature of the mixture of ferric chlorideand steam, and. maintaining the mixture of gaseous ferric chloride andsteam at the said lowered temperature until a substantial portion of theferrie chloride has been reconverted to ferric oxide by a reversal ofthe original reaction.

4. In a method of obtaining ferric oxide from a composition in which itis contained, those steps which consist in heating the composition to atemperature below the melting point of ferrie oxide but above thetemperature at which ferric chloride Volatilizes, eiecting a contact ofhydrogen chloride gas with the heated composition to produce a gaseousmixture of ferric chloride and steam, separating the gaseous mixturefrom said composition, lowering the temperature of the gaseous ferriechloride and steam to a temperature above the temperature at whichferrie chloride condenses, so limiting the hydrogen chloride gasutilized in proportion to the gaseous ferric chloride formed that afterseparating the ferric chloride and steam from the composition, asubstantial degree of reversal of the original reaction is effected uponthe lowering of the temperature of the mixture of ferric chloride andsteam, maintaining the mixture of gaseousI ferrie chloride and steam atthe said lowered temperature until a substantial portion of the ferriechloride has been reconverted to ferrie oxide by a reversal of theoriginal reaction, and recirculating the hydrogen chloride formed by thesaid reversal back into said mass for the treatment of further amountsof the composition.

5. The method of continuously separating ferric oxide from its oreincluding a gangue material which comprises establishing a mass of saidore, heating said mass to a temperature above the temperature at whichferrie chloride Volatilizes and below the melting point of ferrie oxide,continuously passing hydrogen chloride gas through and in contact withsaid mass to produce a gaseous mixture of ferric chloride and steam,Continuously removing said gaseous mixture from said mass, lowering thetemperature of said gaseous mixture to a point not lower than thevolatilization temperature of ferric chloride and causing a reversal ofthe original reaction and production of solid ferric oxide and gaseoushydrogen chloride, recovering said ferric oxide, and recirculating saidhydrogen chloride back into said mass for the treatment of furtheramounts thereof.

URBAN E. BOWES.

